T-Mobile argued in a court briefing today that text-messaging services are not subject to the same regulations as voice services, in defending itself against a lawsuit filed by a text-message marketing company.

Last week T-Mobile was sued by EZ Texting, a company that runs marketing campaigns for various clients that want to send group text messages. In the suit, EZ Texting claimed that T-Mobile pulled the plug on its service after learning it was running a campaign for a client called Weedmaps.com.

However, T-Mobile said it yanked EZ Texting's messaging code because it was supposed to get prior approval for all marketing campaigns run over its network, as specified in its agreement with the marketing company. In addition to Weedmaps.com, EZ Texting also failed to get approval for two other services involving party rentals and church services, T-Mobile claimed in its answer to EZ Texting's complaint.

The more interesting debate, however, involves whether text messages should be subject to the same rules as voice calls. The Federal Communications Commission doesn't allow voice operators to block specific calls under the "common carriers" provision of the Federal Communications Act of 1934, and T-Mobile argued that text messages aren't protected by that law.

However, as you might have noticed, communication has changed just a tiny bit over those last 76 years, prompting questions as to whether modern communications carriers should be subject to the same rules. The FCC has yet to make a decision on that score after being petitioned in 2007 to modernize its regulations.

Updated 12:15 p.m. PDT: Here's a copy of T-Mobile's filing with the court.